In Starcraft II Is there a strategy to get all the upgrades in the Campaign

Although there are other answers about upgrades, I could advise about mercenaries. From my perspective the most valuable are siege tanks and battle cruiser. I would save money from hiring other stuff. They are not much better and die relatively quickly.

And in short: is it possible to get all upgrades? If in one campaign - short answer "no". But if you OK to bother with earning moneys via passing same missions 5-10 times just to get research points to be converted into money - you could try. Although I don't see any value in that.

EDIT:

Sorry. To be honest I must to say I didn't try to earn more research points. But I read that it will works ONLY after getting 25 Zerg/Protoss points. Only after that time you could try to earn more. But I would suggest to play in usual way (probably on casual level) to pass 10-15 missions and to get 1M credits. Made a save and after that do 1 upgrade line - get achievement, reload. Do another upgrades line ...